This invention relates to a belt and pulley drive apparatus and method for permitting a change in speed ratios between first and second rotating members without the removal and replacement of gear pulleys. The invention has particular application on a precision winder. A precision winder is characterized by a precise relationship between the traverse assembly and the chuck assembly. The relationship is expressed in terms of a "wind ration." The wind ratio is determined by multiplying the number of loops in one stroke of the traverse across the yarn package from one end to the other by two. This relationship is varied somewhat by the variance from the exact wind to establish the spacing of adjacent wraps, referrd to as the "gain." A particular wind ratio is selected depending upon the desired characteristics of the yarn package and the type of yarn to wound.
The ratio is established on the winding machine by the selection of appropriately sized pulleys, typically driven by timing belts. An electric motor drives both a traverse assembly and a chuck assembly off of a single shaft by means of concentrically mounted pulleys. In all, four pulleys establish the speed of rotation of the chuck and the speed of the traverse--the two pulleys on the motor shaft and driven pulleys on the traverse and chuck assemblies.
The prior art method of changing the wind ratio involves the calculation of the required pulley sizes, removing all four of the pulleys from the winder and replacing the pulleys with four other pulleys which give the required wind ratio. This requires a substantial period of time, especially when a large number of machines must be changed on short notice within the time requirements of a production schedule. Changing the pulleys in this manner also requires a large stock of replacement gears in a large number of sizes. It has also been observed that maintenance personnel will make mistakes in a certain percentage of cases, requiring further changes and consequent loss of production.
While there is a virtually endless number of actual wind ratios, a relatively small number are adequate for most purposes. There is also an extremely large number of combinations of pulley combinations within the usual range of pulley sizes which will give desired wind ratios. Heretofore, the large number of combinations has required that the pulley sizes be calculated manually and the resulting pulley sizes installed on the winder. As a practical matter this always requires the replacement of all four pulleys, as described above.
As a first step in making a substantial improvement in the efficiency with which wind ratios are changed, a computer program was devised which generates combinations of pulley sizes in tabular form for a given set of operating criteria. In reviewing this data, it was discovered that in a percentage of cases, perhaps 20-30 in from several hundred to several thousand pulley combinations, the motor pulley which drives the chuck assembly and the chuck pulley are the same size for several different wind ratios, with the variation in wind ratio being the result of a change in only the motor pulley which drives the traverse assembly and the traverse pulley. In view of this discovery, the winder can be constructed with a single chuck pulley and the motor pulley which drives the chuck. A desired number of variant wind ratios can be installed on the winder by placing from two to four pulleys concentrically on the motor shaft for driving the traverse assembly, and also placing from two to four pulleys concentrically on the traverse assembly. These pulleys are selected from the computer generated tables referred to above. The wind ratio changes can now be made by simply changing the timing belt from one set of pulleys to another without removing and replacing pulleys.